In fact it is the oposite, metro and RER are more and more crowded.
It is not the 10,000 velib that can carry the millions of passengers that transit inside inner Paris.
If my picture seem quite empty it is because it is the off peak hours.

Take the subway or RER in rush hours in you will understand, the RER A becaume more and more overcrowded like the RER B, line 13, line 1, line 4, line 3...
The metro and RER traffic are in boom. Velib carrying in one years less than the metro and RER system carry in one day.